1. Field of the Invention
The present invention relates in general to electrochemical cells, and more particularly, to electrochemical cells that have an ionomer binder associated with the anodic and/or cathodic electrodes, to, in turn, enhance the electrochemical stability and performance of the electrochemical cell.
2. Background Art
Electrochemical cells have been known in the art for several years. Furthermore, lithium ion secondary electrochemical cells having electrodes with an active material incorporated into a polymeric binder are likewise well known. While electrodes using one or more conventional polymeric binders are known in the art, their solubility characteristics in common electrolyte solvents used in lithium/lithium ion based secondary electrochemical cells, as well as their poor adhesion to an associated current collector remain problematic. In particular, conventional polymeric binder materials, such as poly(vinylidenefluoride) (PVDF), polytetrafluoroethylene (PTFE), ethylenepropylenediene-methylene (EPDM), as well as conventional copolymeric binder materials, such as poly(vinylidenefluoride)/hexafluoropropene (PVDF/HFP), are sufficiently soluble in commonly used organic solvents that swelling of the binder material is readily observedxe2x80x94especially at elevated temperatures. Upon swelling of the binder material, conductivity between particles within the electrode active material can be substantially adversely affected. Moreover, swelling of the binder material can lead to loss of contact between the active material and an associated current collector, thereby further adversely affecting the electrochemical performance of the electrochemical cell, or in some cases rending the electrochemical cell non-operative.
Accordingly, it is desirable to provide an ionomer binder material suitable for use in association with an anodic and/or cathodic electrode for use in an electrochemical cell that is sufficiently insoluble in conventional organic electrolytes used in lithium/lithium ion based secondary electrochemical cells. It is further desirable to provide a binder material suitable for use in an anodic and/or cathodic electrode of a secondary electrochemical cell that exhibits enhanced adhesion to an associated current collector relative to conventional, non-ionomer binder materials.
These and other objects of the present invention will become apparent in light of the present specification, claims, and drawings.
The present invention is directed to an electrode for use in an electrochemical cell comprising: (a) a current collecting substrate; and (b) an electrode active material associated with at least a portion of the current collecting substrate, wherein the electrode active material is at least partially dispersed within an ionomer binder.
In a preferred embodiment of the present invention, the ionomer binder is substantially insoluble in polar aprotic organic solvents.
In another preferred embodiment of the present invention, the ionomer binder is substantially insoluble in a solvent selected from the group consisting of propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, and mixtures thereof.
In yet another preferred embodiment of the present invention, the ionomer binder exhibits enhanced adhesion with an associated current collector relative to a non-ionomer binder.
Preferably, the ionomer binder comprises lithium 2-acrylamido-2-methyl-1-propane sulphonate (LiAMPS), a combination of LiAMPS and N,N-dimethylacrylamide (DMAA), and/or a combination of DMAA-co-LiAMPS copolymer and PVDF.
In accordance with the present invention, the electrode active material may be cathodic and comprise, for example, a transition metal oxide, a doped transition metal oxide, and/or a mixed transition metal oxide, optionally mixed with a carbonaceous material, such as carbon black graphite, etcetera. The electrode active material may also be anodic and comprise, for example, a carbonaceous material, such as graphite, MCMB mixed with carbon black, etcetera.
The present invention is further directed to an electrochemical cell comprising: (a) an electrolyte; and (b) a first electrode and a second electrode, wherein at least one of the first and second electrodes comprises: (1) a current collecting substrate; and (2) an electrode active material associated with at least a portion of the current collecting substrate, wherein the electrode active material is at least partially dispersed within an ionomer binder.
The present invention is also directed to an electrochemical cell consisting of: (a) an electrolyte comprising a salt, at least partially dissolved in a solvent preferably selected from the group consisting of propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, and mixtures thereof; and (b) a first electrode and a second electrode wherein at least one of the first and second electrodes comprises: (1) a current collecting substrate; and (2) an electrode active material, wherein the electrode active material is associated with at least a portion of the current collecting substrate, and wherein the electrode active material is at least partially dispersed within an ionomer binder comprising LiAMPS.
A process for fabricating an electrochemical cell is additionally disclosed which comprises the steps of: (a) providing a first electrode having a current collecting substrate and an electrode active material associated with at least a portion of the current collecting substrate, wherein the electrode active material is at least partially dispersed within an ionomer binder; (b) providing a second electrode with or without the ionomer binder; (c) providing an electrolyte; and (d) configuring the first electrode, second electrode, and electrolyte such that the electrodes are spaced apart from one another yet in electrical communication through the electrolyte.